Auckland could be hit by power cuts by 2007, Vector head Mark Franklin has warned the Government.

In a letter to Energy Minister Trevor Mallard, Mr Franklin describes his "ever-growing concern at the lack of generation and transmission investment to ensure a secure and reliable supply of electricity into the Auckland region".

The letter, obtained by the Herald, was sent to the minister just a week after he extended the deadline for the Electricity Commission to approve or decline Transpower's Waikato pylon project from September to the middle of next year.

Transpower wants the line built by 2010, to supply the growing thirst for power in the Auckland region.

Vector is the lines company that takes electricity from Transpower's national grid and distributes it throughout the region.

"Given we are told new capacity is required into the Auckland region by 2010, the process now seems to cut things extremely fine," Mr Franklin says in the letter.

The 2010 date was based on projections of load growth and assumptions surrounding existing power station plant availability and production.

"There seems to be little recognition that should, for example, a generation plant in the region become unavailable for an extended period of time (as happened many times in the past) then consumers may face outages as early as 2007."

Mr Mallard yesterday rejected the claims, saying there were "many different views on when Auckland will reach a critical time in terms of security of supply, and all rational advice I have received suggests that 2007 is well off the mark".

Transpower's assessment was that supply issues "would reach a more critical stage" in 2010 if no other steps were taken.

"I would also note that the Resource Management Act process, which Transpower must also go through, was never expected to be concluded this year, so any suggestion that my announcement has triggered a real slowdown in the process is questionable.

"The suggestion that the lights are going to go out in 2007 is nonsense."

Mr Franklin says "significant security-of-supply issues were worsening each year", with Vector "on the brink of being forced to shed customers because of transmission and generation constraints".

Transpower had just told it that summer voltage concerns it had been exposed to since 1998 now extended into the winter.

A Vector spokeswoman yesterday said Mr Franklin did not want to comment on the letter as it was "a private document that was not for public discussion".